A wireless device may access a wireless wide area network (“WWAN”) that provides voice, data or other services to the wireless device. The WWAN may include multiple access points throughout its coverage area, which allow a wireless device to travel among different physical locations while still remaining within the coverage area of the WWAN. As a wireless devices changes locations it might remain within the coverage area of the WWAN but move from a portion of the WWAN served by one access point to another portion of the WWAN served by another access point.
As the wireless device moves out of range of one access point and into range of another access point, the wireless device might handoff between the access points. For example, the WWAN might be a wireless telecommunications network, and the access points might be base transceiver stations (“BTSs”). In this case, the wireless device might handoff among different BTSs as it moves throughout the coverage area of the wireless telecommunications network. Various different types of handoffs, such as hard or soft handoffs, are possible depending on the particular type of WWAN.
The Internet Protocol (“IP”) is one protocol the wireless device might use when accessing the WWAN and communicating with one or more entities on the WWAN or on another network via the WWAN. IP defines an addressing system in which a wireless device might be assigned a unique address that can be used to route data packets to and from that wireless device. That is, the IP address can be a globally routable address. A given IP address, however, is typically associated with a specific IP sub-network, which is a logical network defined for routing IP packets to their assigned devices.
As the wireless device moves among different access points in the WWAN, the wireless device might move among different IP sub-networks. Mobile IP is an extension of IP that allows a wireless device to roam among different IP sub-networks while still receiving packets addressed to its assigned IP address. That is, even though the wireless device might move to an IP sub-network that is different from the IP sub-network for its IP address, the wireless device can continue to use that IP address and to receive packets addressed to the IP address.
Usually an IP sub-network is served by a network access server (“NAS”), which can provide Mobile IP services to wireless devices on the IP sub-network. In some WWANs, the network access server might be a packet data serving node (“PDSN”); however, other types of network access servers might be used, and the particular type of network access server used might vary depending on the particular type of WWAN.
In Mobile IP terminology, a network access server might serve as both a “foreign agent” (“FA”) and a “home agent” (“HA”) to wireless devices, although this functionality might be distributed among one or more other entities. It is a home agent with respect to wireless devices having IP addresses on its IP sub-network, while it is a foreign agent with respect to wireless devices having IP addresses on different IP sub-networks.
As a home agent, a NAS can receive packets addressed to a wireless device that has its IP address on the same IP sub-network as the home agent. When the wireless device is on its home IP sub-network, the home agent can forward the packets directly to the wireless device on its home IP sub-network. When the wireless device has roamed away from its home IP sub-network to a foreign IP sub-network, the home agent can forward the packets to a NAS acting as a foreign agent for the wireless device on the foreign IP sub-network.
As a foreign agent, a NAS can receive a registration from a wireless device that has roamed away from its home IP sub-network to the foreign IP sub-network of the foreign agent. The foreign agent can in turn notify the wireless device's home agent of the wireless device's current location on the foreign IP sub-network. Packets addressed to the wireless device may then first be routed to its home agent, which in turn uses the registration to determine that the packets should be forwarded to the foreign agent. The foreign agent receives the packets and then sends them to the wireless device's current location on the foreign IP sub-network.
A wireless device might change locations, thereby moving among one or more different IP sub-networks. One of the IP sub-networks might be served by a HA for the wireless device, and the other IP sub-networks might be served by respective FAs for the wireless device. As the wireless device moves among these IP sub-networks, it can alter is registration with its home agent or a foreign agent. For example, the wireless device might currently be registered with a first foreign agent on a first IP sub-network. The wireless device might the move to a second IP sub-network, which is served by a second foreign agent.
The wireless device might detect the presence of the second foreign agent in a variety of different ways. The wireless device might receive from the second foreign agent an agent advertisement message, which foreign and home agents can periodically transmit in order to signal their presence to wireless devices. Alternatively, the wireless device might transmit an agent solicitation message and in turn receive a response from an available home or foreign agent, such as the second foreign agent. Other methods might also be used.
After detecting the second foreign agent, the wireless device might initiate a Mobile IP re-registration with the second foreign agent. That is, instead of continuing its registration with the first foreign agent, the wireless device might switch its registration to the second foreign agent. Thus, re-registration can refer to the process of switching from being registered with one agent (e.g., either a FA or a HA) to being registered with another agent. During re-registration, the second foreign agent can notify the wireless device's home agent of its new location. The home agent then begins forwarding packets for the wireless device to the second foreign agent instead of the first foreign agent.
In the WWAN, multiple access points might be served by a single NAS. Thus, the access points might all be on the same IP sub-network. A wireless device moving among these different access points might then remain on the same IP sub-network, and therefore it would not need to update its Mobile IP registration with a different NAS as it roamed among these access points. When the wireless device eventually hands off to an access point served by a different NAS, the wireless device would then need to update its Mobile IP registration with the new NAS. This re-registration typically occurs regardless of whether the wireless device is currently participating in a Mobile IP session.
In some instances, the wireless device might be located at a boundary between areas served by different access points. The access points might be located on different IP sub-networks and served by different NASs. When the wireless device is located at this boundary, whether the wireless device is stationary or moving, it might handoff back and forth between the two access points in a sort of ping pong effect. For example, the relative signal strengths of the RF signal received from the access points, or other factors used in determining whether to initiate a handoff, might be approximately equal.
Small changes in the location of the wireless device, variations in atmospheric conditions, other a variety of other effects might cause corresponding slight changes in the relative signal strengths of the access points. And, these effects might continuously, although possibly only slightly, alter the relative signal strengths of the RF signal received from the access points as detected by the wireless device. Since the signal strengths might be approximately equal, these small changes might cause the two signals, within a relatively short period of time, to oscillate back and forth around a point set to trigger the wireless device to handoff between the access points. Each handoff might in turn each cause the wireless device to initiate a Mobile IP re-registration with a NAS for the respective access point currently serving the wireless device. These re-registrations might consume WWAN resources, consume battery power in the wireless device or have other adverse effects.
Therefore, there exists a need for an improved method and system for Mobile IP registration by wireless devices handing off between access points in a WWAN.